ICMCTF1998 Session G5-2: Hard Coating Applications; Cutting, Forming and Autolubricated Tools (2)

Hard coatings to arrest or slow down wear, improve productivity and product quality are now well established in single point tools (HSS and carbide). However the same is not true for multi-point cutting tools. The paper examines the progress made in low value high volume (bandsaws, holesaws) and high value low volume (circular saws, broach tools) products. Whilst some successes are reported there are some continuing disappointments in tool life improvement and performance owing to the lack of systems approach.

The author gives examples of products and has identified parameters and processes which tool manufacturers and coaters should jointly address to fully exploit the advantages of surface engineering technologies.

The paper should prove useful and be of interest to material suppliers, tool manufacturers and surface coaters.

The needs for greater productivity or to press difficult to-cut workpiece materials call for the development of new, higher performance press and dies capable of higher tooling life or pressing conditions.

In this paper the performance of different HSS punching dies coated with innovative mono and multilayer Arc cathodic PVD processes are presented.

In particular the innovative PVD coatings have been developed with the PLATTIT PVD cathodic arc method, and the novelty is the development of auto-lubricant coatings for dry dies applictions. Results of industrial tests and investigations into wear mechanisms for different coated dies in comparison with the performance of standard coated and uncoated dies will be presented and discussed.

The aims of the paper are to present some data related to the characterisation of innovative low friction hard duplex PVD coating for hobs cutting tools, and to present the results of high performance and dry machining tests performed with different HSS hobs coated with these innovative PVD layers in comparison with standard PVD coatings.

In particular the innovative PVD coatings have been developed with the PLATIT cathodic arc technology. The novelty is the development of auto-lubricant, low friction and hard duplex coatings, for hobbing cutting tool applications.

For testing the different coatings in heavy conditions we have chosen high speed and dry cutting tool operations for machining difficult-to-cut materials: this matter is very important and strategic for the industry because due to environmental, health and economic considerations thre is a strong need, today, to replace the presently used machiing technology based on synthetic lubricants by a technology based on high speed and lubricant-free machining. Results of tool life tests, investigations into tool wear mechanisms for different coated hobs will be presented and discussed.

Ti_0.43Al_0.42Cr_0.03Y_0.02N deposited by the combined steered arc/ unbalanced magnetron deposition technique (ABS) exhibits high oxidation resistance and stable chemical composition of the coating to substrate interface up to temperatures of 900°C[1] thus guaranteeing reliable adhesion in extreme thermal conditions. Hardness values at room temperature are HK 2700 associated with HRc "1" and lc ~ 45N.

These coatings have been applied to a range of differently shaped endmills of differing dimensions fabricated from sub-micro grain 10% Co cemented carbide material. All cutters were manufactured to concentricity levels between 4 and 6 μm dependent upon size. All tools beyond a diameter of 6mm were coated with Ti_0.43Al_0.52Cr_0.03Y_0.02N of 3 to 3.5 μm in thickness. Various types of two-flute ball and four-flute corner radius endmills have been tested in steels of up to HRc 62. Cutting conditions can be varied in speed up to 24000rpm, linear feed rates up to 7.5 mmin^-1 in a completely dry cutting operation.

{1}L.A. Donohue, I.J. Smith, W.-D. Münz, I. Petrov and J.E. Greene, ICMCTF '97, to be published in Surf. Coat. Tech.

Electron beam evaporation PVD is a widely used commercial process that has advantages in terms of: 1) Low Evaporant Cost, 2) Smooth Coatings, 3) Versatility, 4) No Spitting and 5) Low Water and Power Costs.

However, evaporation of alloys to form tertiary coatings such as TiAlN is unreliable due to preferential evaporation of the alloying element with the higher vapour pressure.

Dual evaporation, with independent real-time control of the coating composition, gives the above advantages plus the ability to create variable composition throughout a coating and from cycle to cycle.